Legal advice reportedly sent to David Cameron warns that church could be sued under human rights legislation if they refuse to allow the services to proceed.

Exemption granted to the Church of England by the Coalition Bill to prevent it having to conduct gay marriages is “eminently challenge-able” in the European Court of Human Rights.

It also warns that the Government’s insistence that protections put in place for other religious groups who don’t want to marry homosexuals could be undermined by evolving European human rights law.

The warnings, written by Aidan O’Neill, a leading human rights lawyer at centre-left Matrix Chambers, argues that churches that refuse to marry homosexuals would be banned from using council facilities such as village halls.

Other legal opinions commissioned by opponents have argued that teachers could face disciplinary measures under equality laws if they refuse to promote same-sex marriage once the change has been implemented.

Lord Carey warned the plans will lead to “serious and wide-ranging conflict between religious institutions and local authorities”.